perf, cpu hotplug: Use cached value of smp_processor_id()

The perf_cpu_notifier() macro invokes smp_processor_id()
multiple times. Optimize it by using a local variable.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: peterz@infradead.org
Cc: acme@ghostprotocols.net
Link: http://lkml.kernel.org/r/20121016075817.3572.76733.stgit@srivatsabhat.in.ibm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>